Cognitive Radio Based NOMA for The Next Generations of Wireless Communications

In this paper, cognitive radio (CR) based on non-orthogonal multiple access (NOMA) is considered over frequency non-selective Rayleigh fading channels. The two techniques are merged for the sake of improving the performance of multiuser wireless communications. Moreover, CR and NOMA can improve significantly the spectrum utilization and spectrum efficiency, respectively, for the next generations of wireless communications. Furthermore, NOMA can enable CR to work without the need to implement spectrum sensing as a traditional CR works. This can be achieved by sharing the available channels among different users by utilizing simultaneously the same frequency band, but with different power allocation factors (PAF) in the power domain. Additionally, CR-NOMA is proposed in this paper by giving a primary user the priority to communicate with the base station (BS) with its required target rate without any effect on its performance, while a secondary user can use the service with its minimum required rate in the presence of the primary user. This can be achieved by arranging the PAF to control this process. Different scenarios have been considered for two users, and simulation results demonstrate that the primary user has the ability to keep its target achievable rate with acceptable outage probability, while the secondary user can be served simultaneously with satisfactory performance in the presence of the primary user.